This invention relates to a conveyor system and, more particularly, to a conveyor system which can be operated from a power supply of smaller capacity than prior art system.
An example of prior art conveyor system includes a pair of frames facing each other with a spacing disposed between them. A number of conveyer rollers are mounted between the two frames, being disposed adjacent to each other. The conveyor system is divided into a plurality of zones arranged along the direction in which articles are to be conveyed by the conveyor system, and each zone includes a plurality of rollers. One roller in each zone is driven to rotate by a motor. Current is supplied from a power supply to each of the motors. The capacity of the power supply is equal to the maximum current which could be supplied to one motor multiplied by the number of the motors used.
Such maximum current flows in each motor only when the motor is started or locked, and the power supply supplies current to its maximum capacity only when all of the motors in the conveyor system are started or locked at the same time. However, it hardly occurs that all of the motors are started or locked simultaneously with each other, and, therefore, a power supply large in capacity and, therefore, in size has raised the manufacturing cost. However, if such a large capacity power supply is simply replaced by a smaller capacity one, one or more motors must be stopped when current exceeding the allowable capacity of the power supply flows. Stopping motors randomly may disadvantageously interrupt the transportation of articles.
An object of the present invention is to provided a conveyor system which can be driven from a small capacity power supply, with its conveying action not interrupted due to the use of such small capacity power supply, and which can be manufactured at a low cost.
A conveyor system according to the present invention includes a plurality of rollers arranged side by side in a plurality of zones arranged from the upstream toward the downstream of the conveyor system.
The conveyor system includes also a plurality of motors, each driving at least one roller in each zone so that an article can be conveyed to pass the zones successively. Each motor can be mounted in a space within the associated roller or can be mounted outside the associated roller.
A plurality of article detecting means are provided for respective ones of the zones. The article detecting means develops an article-representative signal when an article is present in the zone associated with that article detecting means. Any of various types of article detecting means can be used. For example, optical detectors, ultrasonic detectors, or magnetic detectors may be used.
Hereinafter, a zone in which an article is present, or being conveyed, is sometimes referred to as loaded zone.
Current detecting means is provided, which detects the sum of current flowing through the operating, or rotating, motors, and develops an excessive-current representative signal when the sum of the currents exceeds a predetermined reference current value.
Control means is connected to the respective article detecting means and to the current detecting means. The control means operates, when the excessive-current representative signal is present, to allow such currents to be supplied to a plurality of motors that the sum of the currents is below a predetermined allowable current value. These plural motors include the ones in the loaded zones where those articles first and second in sequence of successive articles being conveyed are present. The predetermined allowable current value may be equal to the predetermined reference current value. Alternatively, the reference current value may be the allowable current value multiplied by a predetermined factor smaller than unity. The control performed by the control means is repeated, for example, at predetermined time intervals.
The control means may include motor drive means for each of the motors, current adjusting means for adjusting the current to be supplied to each motor drive means, and judging means for judging which one or ones of the current adjusting means should be caused to supply current, based on the excessive-current representative signal and the article-representative signal. The judging means may include determining means for determining motors which should be normally driven based on the article-representative signals, and selecting means for selecting a motor to be actually driven out of the motors determined by the determining means.
When the sum of the currents flowing in the currently operating motors of the conveyor system exceeds the reference current value, the maximum value of the sum of the currents flowing in the motors is limited to the allowable current value. Thus, a power supply small in capacity and, therefore, small in size can be used, which reduces the manufacturing cost of the conveyor system. The sum current limitation is carried out in such a manner that current can be continuously supplied to the motors in those loaded zones in which the first and second articles on the conveyor systems are being conveyed, so that the first and second articles continue to be conveyed even when the current limitation is performed. In this case, current is not supplied to the motors in those loaded zones in which the third and succeeding articles are being conveyed.
The control means may be so arranged that a predetermined largest proportion of the allowable sum current (hereinafter referred to as largest proportion current), at the maximum, can be supplied to the motor in the loaded zone in which the first article is being conveyed. Accordingly, the first article can be conveyed without fail even if it is heavy in weight. In other words, the first article has priority in conveyance over the remaining articles.
The control means may be adapted such that a predetermined intermediate proportion of the allowable sum current (hereinafter referred to as intermediate proportion current), at the maximum, can be supplied to the motor in the zone adjacent downstream to the loaded zone through which the first article is being conveyed. The intermediate proportion current is smaller than the largest proportion current. Needless to say, in this case, the first article is not in the downstream end zone. When the first article reaches the adjacent downstream zone, the current supplied to the motor in this adjacent downstream zone may be increased to the largest proportion current. Because the current flowing through the motor in the adjacent downstream zone before the first article arrives at it is of the intermediate value, a transient current can be small.
The control means may be adapted such that a smallest current proportion, at the maximum, which is smaller than the intermediate current proportion, can be supplied to the motor in the loaded zone through which the second article is being conveyed, so that the second article is conveyed at a low speed. Accordingly, the second article continues to be conveyed even at a low speed, which can reduce the conveying time relative to the time where the second article is stopped.
The control means may be adapted such that the largest proportion current at the maximum can be supplied to the motor in the loaded zone through which the first article is being conveyed and that the intermediate proportion current at the maximum can be supplied to the motor in the loaded zone through which the second article is being conveyed, if the zone through which the first article is being conveyed is the downstream end zone. With this arrangement, the first article can be conveyed through the downstream end zone with the largest proportion current so that the first article priority conveyance can be maintained, and, still, the time required to convey the second article does not increase because the motor for the second article is driven with the intermediate proportion current.
The control means may be adapted such that a current equal to or less than a current proportion smaller than the intermediate proportion current can be supplied to the motor in the zone adjacent downstream to the loaded zone through which the second article is being conveyed. With this arrangement, even if it is so arranged that the current through the motor of the adjacent downstream zone is to be increased to the largest or intermediate proportion current when the second article in the preceding loaded zone reaches it, only a small transient current flows in the motor of the adjacent downstream zone.
The current detecting means may be adapted to detect the sum of currents flowing through the currently operating motors, and develop a first excessive-current representative signal when the current sum exceeds a predetermined first reference current value, and a second excessive-current representative signal when the current sum is equal to or larger than a predetermined second reference current value and smaller than the first reference current value. The second reference current value is smaller than the first reference current value. Then, the control means, when the first excessive-current representative signal is present, make it possible to provide currents only to respective ones of a plurality of motors including the motors in the loaded zones through which articles first and second in sequence are being conveyed. The sum of the currents is equal to or below a predetermined allowable current value. In the presence of the second excessive-current representative signal, the control means enable currents to be supplied to a larger number of motors including the motors in the loaded zones through which the first and second articles are being conveyed, than the number of motors driven when the first excessive-current representative signal is present. The motors to be driven are selected from those which are to be driven when no current limitation is provided. The largest proportion current to be supplied to the motor in the zone through which the first article is being conveyed may be maintained at the value equal to the value of the current to be supplied to it when the first excessive-current representative signal is developed. Also, if the motor in the zone adjacent downstream to the zone through which the first article is being conveyed is adapted to be driven, too, the largest proportion current may be equal to the one supplied to it when the first excessive-current representative signal is developed.
With this arrangement, when the sum current value changes to a value smaller than the first reference current value but equal to or larger than the second reference current value after the motors have been controlled to conduct, for example, an allowable current sum, the number of the motors driven can be increased so that articles can be rapidly conveyed. In this case, the allowable current value may be equal to the one to or below which the sum current is reduced when the sum current exceeds the first reference value.